Orbit
An orbit is the gravitational motion of one object around another (usually larger) object, such as a planet around the sun. Since gravity is a force that gets much weaker with distance (inverse-square law) and orbits follow a centripetal motion (proportional to orbital distance and inverse-square of orbital period) then the period and the radius form a relationship known as Kepler's Third Law: 'The period squared is proportional to the maximum radius cubed'. Earth has an orbital period of 1 year and a maximum orbital radius of about 150 billion kilometres (or 1 astronomical unit: 1 AU). Following Kepler's Third Law, the fast-moving planets close to the sun have orbits increasingly shorter than one year, while slow planets further from the sun have orbits increasingly longer than one year. These periods range from 88 days (Mercury) to 248 years (Pluto). The planetary orbits show a resonance with one another, ensuring that after some number of cycles between any two planets they return to their original positions (see Orbital Resonances). This article also considers the 'self-orbit' of a planet, or the rotation of the planet about its own axis (i.e. the planetary day). |NASA:/SpacePlace/How Orbits Work (A Simulation Game)> Orbit Characteristics Eccentricity (Ellipticity) Orbits tend to be elliptical (oval-shaped), rather than circular, since both objects actually orbit around each other's common centre of gravity, rather than a simple fixed point in space. How elliptical the orbit is is characterised by a number called the eccentricity, circular orbits are not very eccentric (e=0) elliptical orbits range from e=0 to e =1, and if you become too eccentric (e>1) then you end up so far away that you never come back again. Earth has a near-circular orbit currently (e=0.017), which has varied over the last 750,000 years between e=0.05 and e=0.005 as belowEarth's eccentricity graph http://www.museum.state.il.us/exhibits/ice_ages/eccentricity_graph.html due to gravitational effects between the planetsEccentricities change over thousands of years. https://en.wikipedia.org/wiki/Orbital_eccentricity#Examples known as the Milankovitch cycles. The most eccentric planets in the solar system are Pluto (0.248) and Mercury (0.206). Inclination The inclination of a planet's orbit refers to the angle it makes with some reference plane: The ecliptic (the orbital plane of the Earth-Sun), the sun's equatorrial plane or the invariable plane (the average orbital plane of all matter in the solar system). Declination https://www.astrologyuniversity.com/those-wild-out-of-bounds-planets/ Out of Bounds https://www.falconastrology.com/oob.html Out-of-Bounds simply means “outside of the boundary of the ecliptic”, or the path of the earth's orbit around the sun. (This is the apparent path of the sun through the sky.) Those Wild Out-of-bounds Planets August 28, 2016 Pamela Welch A planet is considered out of bounds when its declination is beyond the outer bounds or limits of that of the Sun, i.e. greater than 23 degrees and 27 minutes of declination, either North or South. Out of Bounds: Dates Table - Cafe Astrology .com https://cafeastrology.com/outofboundstablesdates.html Self-Orbit (Planetary Rotation) While planets orbit around the sun, they also spin on their own axis, causing the sun to appear to orbit around them each day (e.g. from East to West on the Earth). This defines the planet's "day" and each planet has days of different length. Interestingly, planets do not seem to show a strong correlation between the length of their day and the distance from the sun (see belowPlanetary rotation speed vs distance from sun http://www.physlink.com/Education/AskExperts/ae477.cfm). Venus is a slow-rotating planet, with days lasting 243 times as long as Earth's, even longer than its short year (225 days). = To do Mention Sedna's extremely long orbit: https://en.wikipedia.org/wiki/90377_Sedna Mention moon orbits, and how Triton's is retrograde: https://en.wikipedia.org/wiki/Triton_%28moon%29 References Category:Astronomy Category:Astrology Category:Unfinished